It is occasionally necessary to construct a heat exchanger having a dimension exceeding the maximum which can be brazed in one assembly. In these circumstances, two heat exchanger core sections which have been previously brazed individually may be joined to obtain a heat exchanger of the required dimensions. In most applications, there is a further requirement that heat transfer between adjacent passages through the heat exchanger be maintained at a relatively uniform and efficient level. However, when two heat exchanger core sections must be joined to obtain a single heat exchanger of the required dimension, it has been found difficult to maintain relatively efficient heat conduction between the passages adjacent their common junction. This is due to the non-planar condition of the two surfaces to be joined, caused by thermal stress occurring when the core sections are separately brazed. Merely bringing the two non-planar surfaces into contact at their high points does not provide adequate heat conduction between the passages adjacent each of these surfaces.
Similarly, if a plate type heat exchanger is damaged, the damaged portion may be removed, and a replacement core section assembled and separately brazed in the aggregate. The problem again arises as to how the replacement core section may be joined to the undamaged core section in a manner which provides acceptable heat conduction therebetween.
U.S. Pat. No. 3,372,453, assigned to the same assignee as the present invention, discloses a method for joining two such heat exchanger core sections, wherein a corrugated metallic heat conductive sheet is placed between the warped side plates of the two core sections to be joined. It has been found, however, that simply compressing the corrugated metallic heat conductive sheet between the two irregular surfaces does not provide complete conformation of that sheet to the irregularities of the non-planar surfaces to provide the required heat conduction efficiency. Mere compression does not cause the yieldable metallic fins of this heat conductive sheet to deform sufficiently so that all the fins are in contact with all parts of the non-planar surfaces of the adjacent heat exchanger core sections.